Batman: The Animated Series: 10 Best Characters Who Only Appeared In One Episode

While not a fan favourite episode, the Underdwellers is a good parody of the tropes of classic Charles Dickens novel Oliver Twist. The Sewer King is a good parody of Fagin, as both run child thievery rackets, training children as pick pockets while treating them poorly.

The Sewer King is one of the best one-time villains as his crimes are absolutely vile, and the no-good sort shows no remorse. Kidnapping children, being abusive towards them and forcing them to be criminals is pretty much as disgusting as a person can be. He would strike the children with fear and he forced them to be silent, as Batman finds "Beware the Sewer King" sprayed across the walls of the sewers.

If that is not bad enough, the Sewer King also provides Batman with a physical challenge, as he has trained pet alligators to do his bidding and attack those who would oppose him.

While Batman is able to eventually defeat the threat, the Sewer King proves to be an evil and cowardly man who provides a challenge for the Dark Knight, and has traumatised a fair amount of children during his underground reign of terror.